Friends fear Jenner will fall apart if her Mom passes.

CaitlynJenner‘s beloved mom is facing her sad last days — and friends fear her death will plunge the sex-swapping reality star into an emotional tailspin.

“Caitlyn seems strong, but she’s very fragile. Her mom, Esther, Is the one person she can rely on,” revealed a source.

” I don’t know what Cait will do without her.”

In an exclusive interview, Esther Jenner told The National Enquirer that she’s battled several life-threatening health woes, including two broken hips, pneumonia and a dangerous lung inflammation called pleurisy in the past 18 months.

“Please send good wishes and prayers to my mom,” the former I Am Cait star recently posted in a message on social media.

Added another source: “Caitlyn is isolated from her kids at this point, and her mother is her emotional lifeline. Losing her would be devastating!”

In a cruel twist, Esther’s decline comes just as she bridged a decades-long divide with her child — who became the world-famous after winning the 1976 Olympic decathlon gold medal as muscle-bound Bruce.

“Bruce was always keeping everybody at arm’s length. Caitlyn is warmer and more ready to give you a hug. We talk on the phone almost every day,” she recently revealed.